Continuously variable transmissions (CVT) and transmissions that are substantially continuously variable are increasingly gaining acceptance in various applications. The process of controlling the ratio provided by the CVT is complicated by the continuously variable or minute gradations in ratio presented by the CVT. Furthermore, the range of ratios that may be implemented in a CVT may not be sufficient for some applications. A transmission may implement a combination of a CVT with one or more additional CVT stages, one or more fixed ratio range splitters, or some combination thereof in order to extend the range of available ratios. The combination of a CVT with one or more additional stages further complicates the ratio control process, as the transmission may have multiple configurations that achieve the same final drive ratio.
The different transmission configurations can, for example, multiply input torque across the different transmission stages in different manners to achieve the same final drive ratio. However, some configurations provide more flexibility or better efficiency than other configurations providing the same final drive ratio.
The criteria for optimizing transmission control may be different for different applications of the same transmission. For example, the criteria for optimizing control of a transmission for fuel efficiency may differ based on the type of prime mover applying input torque to the transmission. Furthermore, for a given transmission and prime mover pair, the criteria for optimizing control of the transmission may differ depending on whether fuel efficiency or performance is being optimized.
Systems and methods are described herein for addressing the complicated and sometimes competing criteria that are addressed in controlling a transmission final drive ratio.